In the setting I'm creating for a game, I've given one of the factions plasma shielding and I'm about to rewrite the code behind their shields from scratch. I wanted to revise the game mechanics to be more in line with how the implemented technologies would behave in the real world.

I'm not quite going to make a 100% realistic space combat game, but I wanted to make sure everything behaved mostly in line with how they would in the real world. If something turns out to be impractical following real world rules, I may just make it impractical in the setting.

The shields in question work by taking the exhaust plasma produced by the ship's fusion reactor(s) and ejecting them around the hull while creating a magnetic field to keep the plasma contained in a shell around the ship. Even without the plasma, the magnetic field is able to protect the pilot/crew from cosmic radiation. The plasma is there to protect from incoming projectiles.


  • Would the magnetic field required to contain the plasma around the ship have any adverse effects on the pilot/crew and other components of the vessel? Would the ship/pilot/crew need any shielding against this? (fun bit of irony in shielding against your own shields)
  • What would the shield look like? Or would it not be visible? Would the pilot/crew be able to see through this shield without some sort of assistance from the ship's computer?
  • Would the energy draw be independent on incoming damage? Or could the shields be pushed by too much damage?
  • Would the ship need to spend any energy to prevent the plasma from cooling in space?
  • How much would the shield alter the aerodynamics of an aircraft flying through atmosphere?

How would the shields interact with the following projectiles? Would any of these projectiles completely ignore the shield? Would certain ones be rendered useless against shields? Would some of them be able to partially bypass the shield?

  • High velocity bullets/slugs
  • Guided and unguided missiles
  • Focused electromagnetic waves
  • High power lasers
  • Plasma based projectiles

I sincerely apologize. There were a lot more questions than I was intending to ask that came up while I was typing this post. If any moderators believe there are too many questions for one post, I can try to split this into a second post.

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    $\begingroup$ It's discouraged to ask multiple questions at once. I would first let us define the shield and then ask a follow up regarding how it would stand up against different projectiles. $\endgroup$
    – Mormacil
    Apr 1, 2017 at 14:22
  • $\begingroup$ Similar discussion that addresses some of your concerns: worldbuilding.stackexchange.com/questions/10910/… $\endgroup$
    – wetcircuit
    Apr 1, 2017 at 14:40
  • $\begingroup$ Alright. I'll split this up later today. $\endgroup$
    – Arvex
    Apr 1, 2017 at 14:56
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    $\begingroup$ I'm curious what could possibly make one think that magnetic fields and plasma could be an effective armor against lead bullets... What is a magnetic field or a hot ionised gas supposed to do to a lead bullet coming at high speed? $\endgroup$
    – AlexP
    Apr 1, 2017 at 15:12
  • $\begingroup$ @AlexP it would presumably work like a kevlar bulletproof vest. Bullets do not magically rebound or turn in a different direction because of kevlar aura, rather the threads hold cohesively together and the bullet's impact is absorbed spreading its force over a larger portion of the vest. There is still considerable blunt force felt under the vest, but hopefully it does not penetrate your body.... Plasma shields would work like layers of viscous water to absorb the projectile forces (or something). $\endgroup$
    – wetcircuit
    Apr 1, 2017 at 16:00

2 Answers 2


All depends on the temperature of the plasma

Fusion plasma can be heated to millions of kelvins. This would be destructive to material projectiles, but would cool extremely fast. It would radiate energy outwards (shining like sun), and inwards (heating the spacecraft skin, and overloading it's thermal management) If your fusion engine is not an absolute torch-drive, and your fuel mass is not high, I don't expect, that such a shield could be sustained for a reasonable time.

Plasma is known for being able to absorb or reflect electromagnetic radiation: https://en.wikipedia.org/wiki/Plasma_stealth

Therefore a plasma shield could defend the craft against electromagnetic radiation. (including lasers) But the usual frequency, below which a plasma is reflective, is normally much lower then that of visible light or x-ray (which could be used in a laser weapon.) To effectively counter laser attacks, much more denser plasmas are needed.

It is very difficult to confine plasma with magnetic fields, even when the magnets can surround the plasma (like in a fusion reactor). So, I expect, that a lot of particles will leak, and will be constantly supplied. If the enemy weapon fire gets absorbed in the plasma, it will heat up. If the equilibrium temperature is too high, its particles can acquire so much velocity, that they leave the magnetic confinement, and the shields gets blown away.

A fully deployed high-temperature plasma shield would saturate the passive EM sensors of the vessel, and only let trough active scans, which have higher frequency, than its Characteristic electron plasma frequency. You want this to be high, since you want to reflect lasers, so the shield would render the ship almost blind.

The only really feasible option seems to be a not-too dense, not-too warm plasma cloud. This could be used for radar stealth, but won't mean effective defence against the most attacks. But at least, it could be sustained, without loosing too much plasma or energy.

For game, I suggest, that plasma shield would have a long charging time, while plasma is building up in a magnetic bottle, which have extremely reflective supermaterial wall too. The more reduce engine thrust, the faster it accumulates, and the more energy you divert to heating lasers, the warmer it gets. In the critical point, it is discharged in a spectacular flash. Depending on its temperature, it would last for some seconds, fully countering EM attacks, and reducing kinetic damage by 4/5. If enough EM attack is recived, it would last a little longer. It causes some bearable thermal damage to the ship.

EDIT: plasma shield vs plasma projectile

I'm a bit skeptical about plasma weaponry. Radiative cooling would mean quite a problem here too, and if the plasma is jut fired from its magnetic cannon, it would dissipate in every direction quickly. But if they solve this by the magnetic fields induced by the currents flowing in the plasma projectile itself, and make a viable short range weapon, some interesting mechanisms might arise.

The effect of such a projectile on the shield would be very variable. Depending on how the confinement fields of the shield and the projectile relate to each other, almost anything can happen. Might the projectile is slowed down, and merges with the shield, making it stronger. Might it gets repelled, and dissipated in the void. Might it cuts trough and hits. A lot of computer simulation, scientific research and spywork would be needed to determine the field configurations of the enemy plasma cannons, and find out the ideal shield magnet configurations to counter them.

Even in battle there is some field for creativity. The shield confinement probably would have poles and stronger areas. So the effect would depend on, what part of the spaceship faces the enemy, when you fire up the shields.


In some extreme situations (like enemy ship grappling us and trying to board) the High-Energy Plasma Flare Shield could be used as offensive weapon too. (If the enemy hull intersects the main volume of the shield, shield discharge could burn it and cause EM damage too.)

  • $\begingroup$ Why direct the hot plasma out and let the inner part condense into a cooler liquid or even solid shell? I mean, if you've got the EM control to build the field that contains the stuff, anyhow, seems it'd be moderately easy to keep the shell magnetically coupled to the ship and use that to help protect from thermal problems. $\endgroup$
    – The Nate
    Apr 1, 2017 at 17:04
  • $\begingroup$ @The Nate Sounds good. I'm not plasma physicist, but i think, that having a liquid or solid plasma shell would mean having large mass in the shield, and further reducs visibility through it. And i think, that radiation and heat conduction will attempt to even out the temperature differences in the shield. $\endgroup$
    – b.Lorenz
    Apr 1, 2017 at 17:54
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    $\begingroup$ (FYI: Plasma can't actually be solid; it's a hotter-than-gas phase. Constrained tightly enough, it might act a lot like it, though.) Some amount of the exhaust must escape for thrust, so there has to be some means of getting it out and away. That said, yeah, it would decrease mass of the system less than not capturing (or even just capturing less) of the plasma. Certainly, the heat would try to even out, but if the outer surface is continually being resupplied when moving, a gradient could probably be maintained. (these are just some ideas that your answer prompted.) $\endgroup$
    – The Nate
    Apr 1, 2017 at 18:02
  • $\begingroup$ I do like this sound of this. I was talking with other developers about turning the shield into an active defense instead of a passive defense/secondary HP bar and they seemed to like the idea, too. It will probably become a temporary invulnerability that shuts almost everything else down. $\endgroup$
    – Arvex
    Apr 1, 2017 at 22:18

It sounds like the sort of idea the Chief Engineer would pull out of a hat to get the Star Trek crew out of a jam, then never be mentioned again even though it worked so well. You may need to devise reasons why it can't simply be used again and again.

Set some rules as a game mechanic, both strengths and weaknesses so the plasma shields work like Rock-Paper-Scissors. It beats some attacks, but is vulnerable to others.

Based on your description, here are some possible mechanics:

  • The ship's regular shields are electromagnetic. This requires power to keep them running. The power level might drop when you use other power-intensive technologies like firing electrical weapons or accelerating.
  • Venting excess plasma from the engines implies you need to wait for the excess to build up. You can't use this defense too often or you actually start to deplete plasma you need to travel/escape.
  • the plasma has it's own electromagnetic properties. Aligned with the magnetic shields effectively makes the shields stronger while using the same amount of power, but at a cost to maneuverability. If it can block particle weapons and missiles, your thrusters will not push against the outside world.
  • Alternately, the plasma has it's own electromagnetic properties and you must use more power to the shields to hold it in place.
  • The plasma shield is so strong conventional weapons are not only destroyed on contact but they are actually drawn to the shield, thus the shield can clear an area of incoming missiles – however, this works both ways: you cannnot shoot out through the shields and your own projectile weapons can be drawn back to you.
  • Once you release the plasma, it explodes. Holding it in a coherent bubble with your shields only delays the explosion, so once shields drop you'll need to move away quickly from the plasma cloud. This might require you to drop your regular shields to stop dragging the plasma with you.

One of the first discussions I read on Worldbuilding was about shields, and the answers provide many ideas for how shields might work and the problems they might have.


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